Currently, strong interest is directed to a double patterning process involving a first set of exposure and development to form a first pattern and a second set of exposure and development to form a pattern between the first pattern features. A number of double patterning processes are proposed. One exemplary process involves a first set of exposure and development to form a photoresist pattern having lines and spaces at intervals of 1:3, processing the underlying layer of hard mask by dry etching, applying another layer of hard mask thereon, a second set of exposure and development of a photoresist film to form a line pattern in the spaces of the first exposure, and processing the hard mask by dry etching, thereby forming a line-and-space pattern at a half pitch of the first pattern. An alternative process involves a first set of exposure and development to form a photoresist pattern having spaces and lines at intervals of 1:3, processing the underlying layer of hard mask by dry etching, applying a photoresist layer thereon, a second set of exposure and development to form a second space pattern on the remaining hard mask portion, and processing the hard mask by dry etching. In either process, the hard mask is processed by two dry etchings.
When dot patterns or thin line patterns having a high aspect ratio are formed using a positive resist film, conventional alkaline development has a likelihood of pattern collapse. A study is then made on the process of forming a resist film as a thin film, forming a hard mask below the resist film, and processing the thin film resist pattern. Typical of the hard mask process is a trilayer process based on a combination of carbon film and SOG film. As the feature size is reduced, even the resist film in thin film form suffers from a more likelihood of pattern collapse.
Formation of a dot pattern by reversal of a hole pattern is under consideration. The dot pattern is produced by forming a hole pattern via development of a resist film, transferring the hole pattern to an underlying film via dry etching, coating SOG thereon, and dry etching so that the portions of SOG buried in holes define a dot pattern. This process requires two dry etching steps, once for transfer of the resist pattern to the underlying film and twice for image reversal of the SOG film buried in holes. If the SOG can be directly buried in the resist pattern, image reversal is achievable by single dry etching. Then the process becomes simple and advantageous in cost.
Recently a highlight is put on the organic solvent development again. It would be desirable if a very fine hole pattern, which is not achievable with the positive tone, is resolvable through negative tone exposure. To this end, a positive resist composition featuring a high resolution is subjected to organic solvent development to form a negative pattern. An attempt to double a resolution by combining two developments, alkali development and organic solvent development is under study.
As the ArF resist composition for negative tone development with organic solvent, positive ArF resist compositions of the prior art design may be used. Such pattern forming process is described in Patent Document 1.
Patent Document 2 proposes an image reversal technology involving forming a positive resist pattern of positive resist material via alkaline development, heating the positive resist pattern for insolubilizing it in organic solvent while maintaining alkaline development capability, coating a film of low alkaline solubility, and effecting development to dissolve only the surface layer of the low alkaline solubility film while leaving the majority of film, and to dissolve the positive resist pattern in alkaline developer. The means of insolubilizing the film in organic solvent relies on a base polymer derived from a methacrylate monomer having 7-oxanorbornane.